Having earlier described tax avoidance as “morally repugnant”, George Osborne
left no doubt in his Budget speech that millionaires whose homes are owned
by offshore companies are firmly in his sights.

What he may not have realised as he announced a charge on such properties was that Samantha Cameron’s stepfather could be among those affected by the proposed tax.

Viscount Astor, who is married to Mrs Cameron’s mother Annabel, has a home on the 19,500-acre Tarbert estate on the island of Jura, off the west coast of Scotland, which is owned by a company registered in the Bahamas.

The estate is a favourite holiday location for the Prime Minister and his wife, who last visited it three years ago.

On Desert Island Discs in 2005, David Cameron said it was “a wonderful place”, adding: “The quality of the peace and quiet is fantastic.”

The Tarbert estate is owned by Ginge Manor House, an offshore company named after the Astors’ home in Oxfordshire.

Under previous rules, buyers could have avoided paying stamp duty by buying shares in the holding company. Houses bought by companies will now have to pay stamp duty at 15 per cent, and the Chancellor plans to bring in a charge on properties already held in offshore companies.

The charge, which comes into force next year, is expected to be £15,000 on homes worth £2 million to £5 million, rising to £140,000 a year for homes worth £20 million or more.

The exact value of Viscount Astor’s estate is not known. But the nearby Ardfin Estate was advertised in 2010 at an asking price of £3.5 million.

The estate was bought by William Waldorf Astor in the 1920s, and was used by his daughter-in-law Nancy Astor, the first female MP, as a bolthole during the war.

Two thirds of the estate was transferred to the ownership of Ginge Manor House in 1968. The final third was transferred in 1979. Stamp duty was paid in each instance.

HM Revenue & Customs has become concerned that such arrangements allow purchasers to avoid stamp duty payments if the offshore company is sold. Because the offshore company remains the registered owner in the UK Land Registry, there is no need to pay stamp duty on the sale.

Around £200 million is thought to be lost to stamp duty avoidance and evasion each year. The new rules are expected to recover around £65 million a year.

The Liberal Democrat peer Lord Oakeshott said: “Having a Scottish estate registered in the Bahamas means that you can avoid stamp duty and capital gains tax. As a fellow peer he should bring his property back onshore now.”

Viscount Astor said he paid rent to the company, which is owned by a family trust. He said: “I would be amazed if we were involved because I don’t think the estate is worth anything like £2 million.

“If it was, then theoretically the company would have to pay the money.”